A density functional theory for Yukawa chain fluids in a nanoslit

Abstract

A weighted density functional theory is developed for Yukawa chain fluids confined in a nanoslit. The excess free-energy functional is separated into repulsive and attractive contributions. A simple Heaviside function is used as the weighting function to calculate the weighted density in both contributions. The excess free-energy functional of repulsive interaction is calculated by the equation of state developed by Liu et al., while the contribution to excess free-energy functional by attractive interaction is calculated using the statistical associating fluids theory for chain molecules with attractive potentials of variable range. For pure fluids, the predicted density profiles near the nanoslit wall are in good agreement with simulations. The effect of cut-off introduced in the weighting function for the attractive part is examined; in addition, the surface excess and partition coefficient are calculated. The density profiles are also predicted for mixtures of two Yukawa chain fluids with different chain lengths, hard-core diameters, fluid-fluid and wall-fluid interactions. This work reveals that it is important to decompose the excess free-energy functional into repulsive and attractive contributions, and a simple weighting function can be used for both contributions.